The invention concerns an apparatus for analyzing a measuring substance which is dissolved in a solvent, comprising a conduit for transporting the dissolved measuring substance from a feed means to a measuring location, wherein the feed means is designed to optionally feed a solvent or a dissolved measuring substance into the conduit.
An apparatus of this type is disclosed in DE 10 2004 029 632.
LC-NMR (hyphenated liquid chromatography nuclear magnetic resonance) or FI-NMR (flow injection nuclear magnetic resonance) can be used to analyse soluble substances. A liquid sample (generally a mixture of a solvent and the substance to be measured) is thereby guided from a feed means through a conduit, in particular, a glass or plastic capillary, to a measuring location in an NMR spectrometer.
The liquid sample is thereby typically pushed by subsequently fed transport solvent and the liquid sample is, in turn, pushed by the transport solvent. A so-called “plug flow” is thereby desired, i.e. the liquid sample moves through the conduit like a plug with flat interfaces relative to the transport solvent which extend perpendicularly to the transport direction.
When the liquid sample advances through the conduit, the sample is spread. The speed of laminar flow is maximum in the center of a capillary and drops off towards the edges, approximately like a parabola. The sample front then assumes an approximately parabolic cross-sectional shape.
When the sample advances, the liquid sample is consequently distributed over an extending section of the capillary, i.e. the concentration of substance to be measured in the conduit decreases. This decreased concentration of substance to be measured deteriorates the signal-to-noise ratio (SNR) of the NMR measurement at the measuring location.
Similar problems also occur in other measuring methods using liquid samples, such as UV (ultra violet) absorption or UV fluorescence.
The “Nanotight Y Connector” by Upchurch Scientific Inc., Catalog of Chromatography & Fluid Transfer Components 2006, page 39, discloses a distributor element for splitting a sample flow from a large capillary into two individual capillaries. This distributor element is used to distribute a liquid sample to two measuring means to which the individual capillaries are guided.
It is the underlying purpose of the present invention to provide an apparatus for analyzing a measuring substance which is dissolved in a solvent, wherein the apparatus improves the signal-to-noise ratio of the analysis.